1. Field of the Invention
This invention relates to an optical encoder, especially relates to the structure and the method of fabricating a sensor head in a reflection-type optical encoder.
2. Prior Art
3-grating system optical encoder has 1st optical grating (i.e.,light source side index grating) for modulating scale irradiation light of a light source, 2nd optical grating which constitutes a scale grating on a scale, 3rd optical grating (i.e.,light-receiving side index grating) and a light-receiving device for receiving the transmitted light from the 3rd optical grating to output displacement signals which have different phases with each other. In such the system, it is also known that the light-receiving device and the 3rd optical grating are integrally formed in a light-receiving device array.
In these optical encoders, when the scale is formed as a reflection-type scale, a light source part and a light-receiving part are disposed at one side of the scale as a sensor head. In this case, the light source side index grating and the light-receiving device array may be integrally formed on a common substrate, and it is desirable in respect of the ease of a miniaturization or manufacture. In such the reflection-type optical encoder, the applicant has proposed an encoder in which index gratings and light-receiving device arrays are arranged in mutually overlapping state, and method of right light-irradiation is used, as structure advantageous to especially a miniaturization (Japanese Patent Application (Kokai) No.9-51998). By this method, the optical encoder can be obtained with miniaturized scale, and the air gap can be made small, whereby the influence of a waviness can be reduced.
However, when a light-receiving element array and an index grating are formed in one sensor board with the domain with which it overlaps mutually, the structure of the sensor board will become complicated. Moreover, a manufacturing process will also become complicated supposing the manufacturing process of a light-receiving device array and the formation process of the index grating.
The present invention is to provide a small and highly efficient optical encoder, and provide the manufacture method of the sensor head of such the optical encoder.
An optical encoder of the present invention has a scale on which a reflection type scale grating is formed at a pitch in a measurement axis direction, and a sensor head for sensing the scale, the sensor head being disposed to be relatively movable along the measurement axis. The sensor head includes, a transparent substrate; a plurality of light-receiving areas which are arranged on the transparent substrate at an interval to output different phase displacement signals, respectively, each of the light-receiving areas having a plurality of light-receiving devices which are arranged in the measurement axis direction to output an identical phase displacement signal; and index gratings which are disposed between the light-receiving areas on the transparent substrate so as to modulate the scale irradiating light.
According to this invention, the sensor head of a optical encoder is constituted by a sensor board having a transparent substrate on which light-receiving areas and index gratings are alternately arranged. Each of the light-receiving areas includes a plurality of light-receiving devices. Since the domains of the index gratings and the light-receiving areas are not overlapped each other, this sensor board structure is simple. Therefore, a small reflection-type encoder can be obtained. Further, since the index gratings can be formed using the same material at least one of the metal electrode used for a light-receiving devices, and metal wiring, the manufacturing process of the sensor head also becomes easy.
In this invention, the light-receiving devices in each of the light-receiving area have a common transparent electrode formed on an obverse of the transparent substrate, the reverse being opposed to the scale. On the common transparent electrode, semiconductor layers are formed to be arranged in such a state that each of the semiconductor layers includes an light-sensitive domain. Metal electrodes are formed on the respective semiconductor layers, and an output signal line, which makes common connection of the metal electrodes, is also formed.
In this case, the semiconductor layers of the light-receiving devices in each light-receiving area may be separated mutually, or may be formed in such an integral structure as to have interconnection portions therebetween. Especially in the latter case, the output signal line can be contacted at the interconnetion portions with a low resistance.
Moreover, in this invention, when the light-receiving areas are arranged in a direction perpendicular to the measurement axis the light-receiving areas may be phase-shifted in the measurement axis direction by an integral multiple of the scale grating pitch. Thereby, the influence of the variation in the irradiation intensity of the scale width direction can be reduced.
According to the present invention, a method of fabricating the sensor head has the following processes; (a) forming a transparent electrode on a transparent substrate, (b) forming a semiconductor layer on the transparent electrode, the semiconductor layer including an light-sensitive domain therein, (c) forming a metal film on the semiconductor layer; and (d) patterning the laminated film of the metal film and the semiconductor layer to form light-receiving areas which are arranged at an interval to output different phase displacement signals, respectively, each of the light-receiving areas having a plurality of light-receiving devices which are arranged in the measurement axis direction to output an identical phase displacement signal, and to form index gratings which are disposed between the light-receiving areas at the same time.
According to the present invention, another method of fabricating the sensor head has the following processes; (a) forming a transparent electrode on a transparent substrate, (b) forming a semiconductor layer on the transparent electrode, the semiconductor layer including an light-sensitive domain therein, (c) forming a first metal film on the semiconductor layer, (d) patterning the laminated film of the first metal film and the semiconductor layer to form light-receiving areas which are arranged on the transparent substrate at an interval to output different phase displacement signals, respectively, each of the light-receiving areas having a plurality of light-receiving devices which are arranged in the measurement axis direction to output an identical phase displacement signal, (e) forming an insulating layer to cover the light-receiving areas, (f) forming a second metal film on the insulating film, and (g) patterning the second metal film to form index gratings which are disposed between the light-receiving areas.